The present invention relates to the reception of bit streams broadcasted on several radiofrequency channels, as for example in Digital Video Broadcast (DVB) environments.
In DVB systems, programs are repeatedly transmitted over several transport streams (TS). Each transport stream is labelled by use of three different tags or identifiers. A network ID identifies the network emitting the stream, an original network ID identifies the network where from the stream is originated and a transport stream ID identifies the transport stream.
Each stream is sent over one or several radiofrequency channels, each channel having a different frequency.
When using an IP protocol, a so-called SI/PSI table, or service table, maps the IP address of the data with frequencies to allow retrieving the data.
Upon reception, the tuner is set to the proper radiofrequency and sorts the packets to retrieve a selected program.
However, the radiofrequency channels are subject to variations due, for example, to environmental changes and to signal fading.
Such changes are bound to increase in a mobile environment where the receiver and/or the environment situation evolve quickly. Furthermore, the tables mapping radiofrequencies and IP addresses are valid only within determined geographical areas. When moving from an area to another, the same radiofrequency will be used to carry different programs.
Usually, the receiver starts by scanning the bandwidth to detect every available radiofrequency channel. Then, a quality indicator is determined for each radiofrequency channel. The receiver locks-on a channel which quality indicator is above a determined threshold and processes the signals carried by that channel.
In existing devices, receivers hold onto a selected channel until a loss of signal occurs, i.e. until the quality is too low for processing. In these situations receivers can either wait until the signal quality increases again, or start over again by scanning the bandwidth. This leads to long delays in the processing when the quality decreases.